A dart game is an interesting exercise equipment which has a dart panel including a bull's-eye and many concentric annular regions and radially divided into many sectorial blocks each of which is related to a specific score.
Early dart games or devices had only one bull's-eye. Afterwards, people developed a dart device having double bull's-eyes by defining a smaller region inside the original bull's-eye so as to make two concentric circular regions; generally, the inner bull's-eye's score is higher than the outer bull's-eye's in order to challenge the player's darting accuracy and to advance the interest of the game.
Relative references found about double bull's-eye device include R.O.C. Utility Model No. 192,984, U.S. Pat. Nos. 4,586,716 and 5,193,817. The U.S. Pat. No. 4,586,716 disclosed a double bull's-eye device formed by engaging an ax/al key way provided on the outer bull's-eye and an extension provided on the rib of the inner bull's-eye. The R.O.C. Utility Model No. 192,984 and the U.S. Pat. No. 5,193,817 correspondingly disclosed a similar double bull's-eye device which is formed by sleeving an inner circular target plate onto an annular support member sleeved onto an outer circular target plate and then securing the annular support member on a target frame with screws; but, such a dart device would have a higher cost due to the tedious assembly with screws.
References:
1. R.O.C. Utility Model No. 192,984 issued to Pan, Jong-Haw on Oct. 11,1992. PA1 2. U.S. Pat. No. 4,586,716 issued to Brejcha et al. on May 6, 1986. PA1 3. U.S. Pat. No. 5,193,817 issued to Pan on Mar. 16, 1993.